Magnetic material



Patented July 3, 1928..

UNITED ,sTATEs FATE-NT OFFICE.

GUSTAF ELMEN, OF LEON IA, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COH- PANY, INCORPORATED, OF NEW YORK,

N. Y., A CORPORATIONv OF NEW YORK.

MAGNETIC MATERIAL.-

Application filed May 29,

, change in permeability at low magnetizing forces in response to changes in temperature.

Another object of the invention is to provide a magnetic temperature controlled device operative in response to changes in temperature for controlling an electrical circuit.

This application is in part a continuation of application, Serial No. 473,877, filed May 31, 1921, Patent No. 1,586,884, June 1, 1926.

Iron is the material which has been almost universallyused in the past for electrical machines and apparatus employing magnetic I circuits, but within recent years compositions of iron with small percentages of silicon have been extensively used for certain urposes, chiefly because they have a permeaility higher than iron alone. These compositions are commonly known as silicon iron or silicon steel.

Still more recently, the present inventor discovered the permalloys, so-called by reason of their very high permeabilities. These consist of nickel and iron which may or may not be combined with another element or elements. Various forms of permalloy,- as well as methods of heat treatment to secure the desired properties, are described in applicants Patents 1,586,884, June 1, 1926, and 1,586,887, June -1, 1926. See also the paper by H. D. Arnold and G. W. Elmen entitled Permalloy, published in the May 1923 issue of the Journal of the Franklin Institute. The permalloys in general exhibit the property of very high permeability at low J magnetizing forcesforces up to a few v4 tenths of a gauss, in most cases.

In applicantsv Patent 1,586,884, June 1, 1926, there is disclosed an alloy comprising two-thirds nickel and one-third copper having a higher permeability than ironat low magnetizing forces. The present application, which is in part a continuation of that patent, relates to magnetic alloys, including the alloy mentioned above, which have a higher permeability at 'low magnetizing 1926. Serial No. 112,450.

forces'than iron. The permeabilities obtainable in these materials are not as high as the permeabilities developed in permalloys when properly heat treated, but are higher than the permeabilities obtainable with iron at magnetizing forces up to a few tenths of 60 I a gauss. These materials may therefore be used to advantage as magnetic elements in signaling circuits and for other purposes in the electrical arts where iron has heretofore been employed.

An important feature of this invention is the use of alloys or compositions of nickel and another or other-elements, as, for example, copper, as magnetic temperature controlled devices operative in response to changes in temperature. Pure nickel has a transformation temperature -of about 350 C. above which it becomes non-magnetic. Just below the transformation temperature there is a very rapid decrease in permeability from the maximum, which occurs at about 320 C. The temperature-permeability curve is also rather steep on the lower side of- 320 C. although the change in this region is less rapid. It has been discovered that by adding copper to the nickel in varyingproportions, the transformation temperature'is gradually brought lower until the point of maximum permeability is brought down to room temperature or less. This holds true only for very low magnetizing forces. At higher magnetizing forces, the peakof maximum permeability becomes less pronounced and finally disappears. I

Similarresults are also obtainable with 99 magnetic materials comprising nickel and other elements. It has been. found that alloys comprising nickel and another metal which forms a solid solution with nickel have, in general, a permeability-temperature characteristic similar to thatof nickel and the nickel-copper alloys. The tempera ture at which the peak permeability occurs, however, depends. upon the particular element employed and upon the percentage'of 9 such element which is alloyed with the j nickel. It has also been found that nickel" alloys have, in general, a lower transformation't emperature than nickel alone, although in "general, nickel-iron and nickel-cobalt duce alloys of nickel and other metals, having an abrupt decrease in permeability at any desired temperature lower than that obtained with nickel itself. Such ma netic materials may be employed in many ifferent situations in the electrical arts for controlling electrical circuits in response to predetermined changes in temperature.

The Various features of the invention will be described in detail in connection with the accompanying drawings, in which: s

Fig. 1 shows perme'ability-temperature curves for nickel and two different nickelcopper alloys at .a low magnetizing force;

Fig. 2 is acurve showing the temperature at which the peak permeability occurs when varying percentages of copper are alloyed with nickel; s Fig. 3 is a curve showing the variations in magnetic induction at a relatively large magnetizing force for various nickel-copper alloys;

Figs. 4 to 7, inclusive, show permeabilitytemperature curves for various other magnetic materials at low magnetizing forces;

Fig. 8 shows the permeability-temperature curve for a particular nickel-copper alloy at a considerable higher magnetizing force; and

Fig. 9 is a diagrammatic illustration of an electrical circuit containing a magnetic temperature controlled element of this invention.

The curves shown in Figs. 1 and 4 to 7, incluslve, are permeability-temperature curves measured at low magnetizing forces with the temperature varying from that of the room .a similar cur ve for an alloy proximately 78 /2% nickel and 2l copto slightly above the magnetic transformation temperature. These curves are obtained by measuring the alternating current permeability at magnetizing forces of about .004 gauss at frequent temperature intervals as the temperature of the alloy is raised gradually until .it becomes non-magnetic. The

frequency employed was 600 cycles per sec ond. A similar curve is obtained with a decrease in temperature. For the partlcular alloys or compositions disclosed in this appllcation, the curves for the ascending temper. Allthree materials have a peak permeability very close to th magnetic transformation point, and beyon that peak temperature the permeability decreases very 10% copper, and curve a is containing ap- -meability-temperature rapidly; The alloys of nickel and copper have a lower magnetic transformation temperature than nickel alone, the transformation temperature decreasing as the percentage of copper is increased. The permeability at room temperature of 25 (1, however, 1ncreases as the percentage of copper 1s mcreased, the permeability at room temperameability at 0 C. It has not been deter-.

mined by test how far below zero temperature this relation continues approximately linear with increasing percentages of copper.

The curve of Fig. 2 shows that it is possible to produce an alloy of copper and nickel in such proportions that the peakpermeability will occur at any desired temperature below that of the peak value of nickel itself, at least down to very low temperatures.

The curve of Fig. 3 illustrates the mag-' netic induction at a magnetizing force of H=100 gausses for varlous m ckel-copper alloys, and shows that the magnetic induction decreases appreciably with increasing percentages of copper at high magnetizing forces. f

Fig. 4 shows the permeability-temperature curves for twoalloys containing nickel and small percentages of iron. These curves are included in order to show that when small percentages of iron are added to nickel, the magnetic transformation temperature becomes higher than that of nickel, but the general characteristics of the curves are substantially the same as for nickel. Similar results are obtained with alloys of nickel and cobalt. F

Figs. 5 to 7, inclusive, show permeabilitytemperature curves "for alloys containing nickel and small percentages of other metals. Fig.5, for example, shows the characteristic curves, for an alloy containing approximate- .ly 97.57% nickel and 2.43% silicon,,an alloy containing approximately 98.65% nickel and 1.35% titanium, and an alloy containing ap-. proximately 98.85% nickel and 1.15% vanadium, respectively. The magnetic transformation temperatures as well as the temperatures of maximum permeability of these al- ;,loys are lower than that of nickel shown by the curve a of Fig. 1.

i Fig. 6 shows curves illustrating the percharacteristics three different alloys in the approximate proportions, of 95.25% nickel and 4.75% manganese, 96.25% nickel and 3.75% molybdenum, and 98.67% nickel and 1.33%

' my patents mentioned above.

are heated in a furnace to a temperature of from about 950 C., to 1100 alloy tantalum. The curves of Fig. 7 illustrate the permeability temperature characteristics of an alloy containing approximately 95.43% nickel and 4.57% chronium, and an containing approximately 96.22% nickel and 3.78% tungsten.

The magnetizing 'force employed in obtaining the permeabilities of the above mentioned alloys is approximately .004 gauss. As the magnetizing force increases, the permeability at low temperatures increases and the peak permeability decreases. This is illustrated by the curve of Fig. 8, showing the pcrmeability-temperature curve for an alloy containing approximately 89.79% nickel and 10.21% copper at a magnetizing force of 2.09 gausses. This particular a 0y has been selected merely for purposes 0 illustration, the results at such magnetiz ng forces for the other alloys being, in general, similar. When the magnetizing force is still further increased to saturation values, the permeability decreases gradually as the temperature is increased from room temperature of about 25 C., to the magnetic transformation temperature.

The heat treatment of the magnetic materials of this invention is in general similar to the heat treatment of nickel-iron alloys involving slow cooling, as described in The alloys (3., and kept; at such temperature until uniform structure is .obtained throughout the material. The material may be left in the furnace after heating and allowed to cool down to room temperature with the furnace, or otherwise cooled at a slow rate, the optimum rate being determined by trial in each case.

The characteristics'of these magnetic materials when subjected to low magnetizing forcesyand particularly the abrupt decrease in. permeability at any desired temperature, render the materials particularly adapted for use in connection with temperature regu lating systems, fire-alarm systems, etc. A system of this general character is illustrated in F ig; 9. This system comprises a source .of electrical energy 10, an indicating or regulating device 11, a line regulating resistance 12and a relay 13 exposed to variable temperatures and equipped in accordance with this invention with a magnetic core of any of the magnetic alloys, depending upon the particular ermeabiIity temperature characteristic desired. The system is so adjusted that at ordinary temperatures the armature of relay 13 is attracted by the magnetism of the relay magnet, against the tension of a suitable spring. When the temperature of the relay reaches a predetermined critical value just above the temperature at which the peak permeability occurs, depending upon the particular magnetic alloy employed as the core material, the permeability of the core material decreases abruptly and the armature is released, closing contact 14'and allowing current to pass through the indicating or regulating device 11. A circuit of this type may be employed in connection With automatic temperature regulating systems. In such case, the magnetic core of the relay 13 will lose its magnetism when it reaches a predetermined critical temperature just above the desired temperature, causing the operation of the regulating device 11, which may be utilized to reduce the temperature of the heating system. When the temperature again becomes normal the core of the relay 13 will regain its magnetism and again attract its armature. thus opening the circuit of the regulating device 11.

It will be evident to those skilled in the art that many different alloys having widely different permeability-temperature characteristics may be employed in accordance with the invention, and that 'the abrupt change inpermcability with changes in temperature may be utilized to advantage for many other purposes without departing from the scope and spirit of the invention.

What is claimed is:

1. A magnetic material comprising nickel and copper and having a higher permeability at low magnetizing forces than iron.

2. A magnetic material comprising nickel and copper in which the copper component comprises from very low percentages up to about one-third of the whole, and having a higher permeability at low magnetizing forces than iron.

3. A magnetic material comprising approximately two-thirds nickel and one-third copper and having a higher permeability at low magnetizing forces than iron.

4. A magnetic material comprising nickel and another element and having a magnetic transformation temperature lower than that of nickel, said material having at low magnetizing forces a permeability which decreases abruptly from its maximum value to substantia-lly zero when subjected to a change in temperature ofless than 10 C. in the neighborhood of the transformation temperature.

5. A magnetic material comprising nickel and another element and having a magnetic transformation temperature lower than that of nickel, said material having at low magnetizing forces an abrupt decrease in permeability at a temperature slightly below its transformation temperature.

6. A magnetic material comprising nickel .and copper, the permeability of which varies greatly in response to slight chaiiges in temperature in the neighborhood of its magnetic transformation temperature.

7. A magnetic material comprising nickel and copper and having at low magnetizing forces a permeability which decreases ab-' ruptly from a maximum to zero in the neighborhood of the transformation temperature. 8. A magnetic material comprising nickel 'andcopp'er and having an abrupt change in permeability at low magnetizing forces when its temperature is varied, the temperaa neighborhood of its transformation temperature, a translating device, and means for operating said device when said element approaches the transformation temperature;

10. An electric circuit including a magnetic element subjected to a low magnetizing -force, said element comprising nickel and copper and having its maximum permeability at a lower temperature than nickel and an abrupt decrease in permeability at a slightly higher temperature, a translating device, and means for ope 'ating said'device when the temperature of said. element exceeds the temperature of maximum permeability;

11. In a control device, a magnetic :ci rcuit including a magnet and cooperating armature, said magnetic circuit including an alloy of nickel and copper'and having a lower magnetic transformation temperature than nickel, the magnetic permeability of said alloyvbeing responsive to temperature changes to cause the operation of said armature in the neighborhood of said transformation temperature.

12. In a control device, a magnetic circuit including a magnet and cooperating armature, and in which an alloy of nickel and copper comprisesa part of the magnetic circuit, the magnetic permeability of said alloy being responsive to temperature changes to cause the operation of said armature.

13. In 'a control device,a magnetic circuit including a magnet and cooperating armature, said magnet circuitincluding an alloy comprising approximately two-thirds nickel and one-third copper, the magnetic permeability of said alloy being responsive to temperature changes ,to cause the operation of said armature.

In witness whereof, I hereunto SllbSCIib(- my name this 28th day of May, A. D. 1926.

GUSTAF W. ELMEN. 

